Assertion (A): In LED \(e^-\)-hole pair recombination gives us photon.
Reason (R): In LED \(e^-\)-hole pair recombination occurs in depletion region.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true; LEDs emit photons when electrons and holes recombine. Reason (R) is false; while carriers cross the depletion region, significant recombination leading to light emission primarily occurs in the quasi-neutral regions (or active layer) under forward bias, not mainly within the depletion region itself.
Assertion (A): In a N-type semiconductor, the number of holes get reduced.
Reason (R): Rate of recombination of holes would increase due to the increase in the number of electrons
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true; in an N-type semiconductor, donor doping increases electron concentration, which, by mass action law (\(np=n_i^2\)), reduces the equilibrium hole concentration. Reason (R) is true; the increased number of electrons in an N-type semiconductor leads to a higher rate of recombination with the minority holes. (R) correctly explains (A) as this increased recombination helps establish and maintain the lower equilibrium hole concentration.
Assertion (A): Electron hole recombination takes place in P-region and N-region of PN Junction diode except in depletion region.
Reason (R): Electric field in depletion region oppose the diffusion.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is generally true in simplified models, where most recombination occurs in the quasi-neutral P and N regions. While some recombination does occur in the depletion region, its contribution to the overall current is often considered secondary for typical forward-biased diodes.
Reason (R) is true; the electric field in the depletion region acts as a barrier, opposing the diffusion of majority carriers across the junction. (R) does not explain the spatial distribution of recombination described in (A).
Assertion (A): Width of depletion region is reduced in forward bias.
Reason (R): In n-type semiconductor majority charge carriers are free electrons while in p-type they are holes.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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When a p-n junction is forward biased, the applied voltage counteracts the internal electric field, causing majority carriers to move towards the junction and reducing the depletion region's width. Thus, Assertion (A) is true.
Reason (R) correctly states the majority carriers in n-type (electrons) and p-type (holes) semiconductors, which is also true. However, Reason (R) does not explain why the depletion region width reduces under forward bias. Hence, both are true, but R is not the correct explanation for A.
Assertion (A): The drift current in a p-n junction is from n-side to p-side.
Reason (R): The diffusion current in a p-n junction is from p-side to n-side.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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In a p-n junction, the built-in electric field points from the n-side to the p-side, causing drift current to flow from n-side to p-side. Thus, Assertion (A) is true. Due to concentration gradients, diffusion current arises from the movement of majority carriers, resulting in a net diffusion current from p-side to n-side. Thus, Reason (R) is also true.
These are two distinct current mechanisms, and R does not explain A.
Assertion (A): P-type semiconductor has high density of holes in valence band while N-type semiconductor has high density of electrons in conduction band.
Reason (R): In N-type semiconductor, as the density of donor atoms (N_D) is increased, the fermi energy level shifts towards the valence band.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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P-type semiconductors have a high concentration of holes in the valence band, and N-type semiconductors have a high concentration of electrons in the conduction band. Thus, Assertion (A) is true.
In an N-type semiconductor, increasing the donor atom density (N_D) increases the electron concentration, causing the Fermi energy level to shift closer to the conduction band, not the valence band. Hence, Reason (R) is false.
Assertion (A): Generally npn transistors are widely used.
Reason (R): In npn transistor the mobility of majority charge carriers is more.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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NPN transistors are widely preferred because their majority charge carriers, electrons, have significantly higher mobility than holes. Higher electron mobility allows for faster switching speeds and better high-frequency performance, making NPN transistors generally more efficient and widely used. Therefore, Assertion (A) is true, Reason (R) is true, and R is the correct explanation for A.
Assertion (A): Output frequency of time varying DC voltage in a full wave rectifier is twice of input frequency.
Reason (R): A center tap transformer increases the frequency of input.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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A full-wave rectifier converts both halves of an AC input into a pulsating DC output, effectively doubling the input frequency. Thus, Assertion (A) is true. A transformer only steps up or steps down voltage and current; it does not alter the frequency of the AC signal. Hence, Reason (R) is false.
Assertion (A): A NAND gate can be obtained by using NOR gates.
Reason (R): NOR, NAND and XOR gates are called universal gates.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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NAND and NOR gates are universal gates, meaning any other logic gate (including NAND) can be constructed using only NOR gates. Hence, Assertion (A) is true. However, while NAND and NOR are universal gates, XOR is not. Therefore, Reason (R) is false.
Assertion (A): Light emitting diode (LED) emits self radiation.
Reason (R): LED are reverse biased p-n junctions.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Concept: LED operation.
LEDs are \(p-n\) junctions that emit light when forward biased due to electron-hole recombination. Reverse biasing does not cause light emission. Thus, Assertion (A) is true, but Reason (R) is false.